Śrāddha-kalpa: Amarakantaka–Tīrtha-Māhātmya and Akṣaya Pitṛ-Tarpaṇa
इन्द्रियाणां मनो घोरं बुद्ध्यादीनां विवर्त्तनम् / अना हारो क्षयं याति विद्यादनशनं तपः
indriyāṇāṃ mano ghoraṃ buddhyādīnāṃ vivarttanam / anā hāro kṣayaṃ yāti vidyādanaśanaṃ tapaḥ
The mind that runs with the senses is fierce, turning even buddhi and the rest; yet non-eating wanes—know anaśana (fasting) as tapas.